1. Field of the Invention
The invention concerns a hyrdrodynamic bearing and more especially, a foil bearing. It also concerns a method for the assembly of a bearing of this type.
2. Description of the Prior Art
In rotating machines of high rotating speed, it is most common to use buoyant fluid film bearings preventing any contact between solid surfaces. These bearings are designed to support and guide the shafts of said machines. The most commonly used type of bearing is the hydrodynamic bearing wherein the fluid film is a film generated by the rotation of the shaft or by the shifting of another part. These hydrodynamic bearings therefore have the advantage of being autonomous.
Most of the time, hydrodynamic bearings are foil-bearings. In this case, thin, curved leaves are fixed in the bore of a bearing body so that they partially overlap one another, and form an internal floating surface forming buoyant corners which generate the creation of a fluid film between the foils and the shaft when the rotation speed of the latter reaches a sufficient value.
To simplify the manufacture and maintenance of bearings of this type, the European patent EP-A-No. 095961 has proposed the making of the foils in the form of independent cartridges which are then inserted into the bore of the bearing body. As described in the European patent EP-A-No. 095961, the bearing is made by manufacturing an independent cartridge designed to form the internal functional unit of the bearing, said cartridge consisting of curved thin foils fixed to one another with overlapping parts, so as to form an independent unit possessing, firstly, an internal floating surface adapted to being placed around this shaft and to establishing the conditions, during the rotation of the shaft, for the formation of a fluid film between the shaft and the internal surface and, secondly, a peripheral external surface with a diameter corresponding to that of the bore of the bearing body, in inserting said cartridge thus obtained in the bore of the bearing body, and in holding it still, during rotation and axial translation, with respect to said bearing body. Thus, to enable the insertion of said cartridge in the bore, it becomes therefore necessary to leave a small clearance between these two elements.
Furthermore, according to a preferred embodiment, the independent cartridge is made by fixing the foils to one another by soldering, notably by means of two soldering spots made at the ends of each foil. Now, since the solderings cause the foils to be solidly joined to one another, they cause deformations at each end of the cartridge. Thus, to enable the assembly of the cartridge inside the bore, a certain clearance has to be provided. However, this assembling clearance gets added to the clearance needed for precise operation of the hydrodynamic bearing. This causes an excessive total clearance under the effect of pressure exerted on the entire central part of the bearing.
An object of the present invention, therefore, is to overcome this disadvantage by providing a precise operating clearance throughout the length of the bearing.